National Aquarium in Baltimore, Baltimore, Maryland

Concierge.com's insider take:

Just as Baltimore's Camden Yards influenced sports stadia across America, the aquarium's 1981 opening represented a watershed moment in urban fish-tank design. Rising five stories from the north side of the Inner Harbor and topped by a distinctive sail-shaped glass atrium, the structure is fins-down the city's most beloved attraction, luring 1.6 million visitors a year. Its exhibits cover the waterfront: In addition to colorful reef fish, there are areas devoted to such ecosystems as western Maryland waterfalls, the Amazon River, Pacific kelp forests, Australia (including a freshwater croc), and a tropical rain forest, complete with exotic birds. There is also a 4-D big-screen theater and de rigueur dolphin show, but the main attraction is the gi-normous Atlantic coral reef exhibit; visitors are treated to 360-degree views of jacks and angelfish while descending a spiraling walkway in the middle of the doughnut-shaped tank. Another theater in the round holds nurse, lemon, and sand-tiger sharks. Every other weekend, Atlantic Edge Dive Center (301-519-9283; www.atlanticedge.com) leads certified divers on a pair of 30-minute plunges inside the Atlantic reef tank and nearby "Wings in the Water," a shallow tray that holds sea turtles and stingrays.